1. IDEAL GAS LAW Brings together gas properties. Can be derived from experiment and theory. BE SURE YOU KNOW THIS EQUATION! P V = n R T

2. The Ideal Gas Law PV = nRT P = pressure (atm, mmHg, torr, KPa) V = volume (in Liters) n = number of moles (mol) R = Universal Gas Law Constant (on STAAR chart) T = Temperature (in Kelvins) CHEMSAVER P 31

3. The Gas Constant R Repeated experiments show that at standard temperature (273 K) and pressure (1 atm), one mole (n = 1) of gas occupies 22.4 L volume. Using this experimental value, you can evaluate the gas constant R = (1 atm* 22.4 L)/(1 mol*273 K) R = PV/nT = (1 atm* 22.4 L)/(1 mol*273 K) R = 0.0821 L ·atm / mol·K = 8.31 L · kPa / mol·K = 8.31 L · kPa / mol·K = 62.4 L · mmHg/ mol·K = 62.4 L · torr/ mol·K CHEMSAVER P 31

4. Using PV = nRT How much N 2 is required to fill a small room with a volume of 960 cubic feet (27,000 L) to 0.98atm at 25 o C? Solution Solution 1. Get all data into proper units V = 27,000 L V = 27,000 L T = 25 o C + 273 = 298 K T = 25 o C + 273 = 298 K P = 0.98 atm P = 0.98 atm R = 0.0821 L ·atm / mol·K R = 0.0821 L ·atm / mol·K

5. Using PV = nRT How much N 2 is required to fill a small room with a volume of 960 cubic feet (27,000 L) to 0.98atm at 25 o C? Solution Solution 2. Now plug in those values and solve for the unknown. PV = nRT n = 1100 mol or 1.1 x 10 3 mol RT RT

6. Using Ideal Gas Law Example What is the volume of 2.30 moles of hydrogen gas at a pressure of 122 kPa and temperature of 20.0 o C? Ans: V = nRT/P 8.31 L ·kPa / mol·K V = (2.30 mol)(8.31 L ·kPa / mol·K)(293K) 122 kPa = 46.0 L

7. Deviations from Ideal Gas Law Real molecules have volume. The ideal gas consumes the entire amount of available volume. It does not account for the volume of the molecules themselves. There are intermolecular forces. An ideal gas assumes there are no attractions between molecules. Attractions slow down the molecules and reduce the amount of collisions. –Otherwise a gas could not condense to become a liquid.

8. This implies: If the volume of space occupied is large and the pressure is low, the behavior of a gas is very close to that of an ideal gas. We will not deal with gases at conditions that make them non- ideal in this class.